How to render individual objects (one per frame)
You can easily do this by assigning an Object ID index to each object that corresponds to the frame in which you want the object to appear. 

Then in the compositor, you set the alpha channel using the IDMask node. The trick is to then add a driver to the Index value so that it uses the frame number as the Index value on each frame change.



To add the driver, right click on the Index field in the ID Mask node, and select Add Driver. Then, with the node still selected, open the Graph Editor and switch to Driver view. The default driver type is Scripted Expression, and all you need to do is enter the value "frame" in the Expr field of the driver settings. Now when you change the active frame on the timeline, the ID Mask node will update the alpha channel to filter out all other objects and just show the object with the Object Index ID that matches the current frame number.